Investigation of three doses of oral insulin-like growth factor-I on jejunal lactase phlorizin hydrolase activity and gene expression and enterocyte proliferation and migration in piglets

Clinical outcome and gut development after insulin-like growth factor-1 supplementation to preterm pigs

BACKGROUND

Elevation of circulating insulin-like growth factor-1 (IGF-1) within normal physiological levels may alleviate several morbidities in preterm infants but safety and efficacy remain unclear. We hypothesized that IGF-1 supplementation during the first 1-2 weeks after preterm birth improves clinical outcomes and gut development, using preterm pigs as a model for infants.

METHODS

Preterm pigs were given vehicle or recombinant human IGF-1/binding protein-3 (rhIGF-1, 2.25 mg/kg/d) by subcutaneous injections for 8 days (Experiment 1, n = 34), or by systemic infusion for 4 days (Experiment 2, n = 19), before collection of blood and organs for analyses.

RESULTS

In both experiments, rhIGF-1 treatment increased plasma IGF-1 levels 3-4 fold, reaching the values reported for term suckling piglets. In Experiment 1, rhIGF-1 treatment increased spleen and intestinal weights without affecting clinical outcomes like growth, blood biochemistry (except increased sodium and gamma-glutamyltransferase levels), hematology (e.g., red and white blood cell populations), glucose homeostasis (e.g., basal and glucose-stimulated insulin and glucose levels) or systemic immunity variables (e.g., T cell subsets, neutrophil phagocytosis, LPS stimulation, bacterial translocation to bone marrow). The rhIGF-1 treatment increased gut protein synthesis (+11%, p < 0.05) and reduced the combined incidence of all-cause mortality and severe necrotizing enterocolitis (NEC, p < 0.05), but had limited effects on intestinal morphology, cell proliferation, cell apoptosis, brush-border enzyme activities, permeability and levels of cytokines (IL-1β, IL-6, IL-8). In Experiment 2, rhIGF-1 treated pigs had reduced blood creatine kinase, creatinine, potassium and aspartate aminotransferase levels, with no effects on organ weights (except increased spleen weight), blood chemistry values, clinical variables or NEC.

CONCLUSION

Physiological elevation of systemic IGF-1 levels for 8 days after preterm birth increased intestinal weight and protein synthesis, spleen weight and potential overall viability of pigs, without any apparent negative effects on recorded clinical parameters. The results add further preclinical support for safety and efficacy of supplemental IGF-1 to hospitalized very preterm infants.

Growth response to growth hormone (GH) treatment in children with GH deficiency (GHD) and those with idiopathic short stature (ISS) based on their pretreatment insulin-like growth factor 1 (IGFI) levels and at diagnosis and IGFI increment on treatment

OBJECTIVES

Some idiopathic short stature (ISS) patients may have varying degrees of insulin-like growth factor 1 (IGFI) deficiency. Others with growth hormone deficiency (GHD) (peak GH < 7 ng/dL after provocation) have normal IGFI levels. Do children with ISS or those with GHD with variable pretreatment IGFI standard deviation score (IGFISDS) have different IGFI and growth responses to recombinant human growth hormone (rhGH) therapy?

METHODS

We studied the effect of GH therapy (0.035-0.06 mg/kg/day) on linear growth and weight gain per day (WGPD) in children with ISS (n=13) and those with GHD (n=10) who have low pretreatment IGFISDS (IGF SDS < -1.5) and compared them with age-matched prepubertal children with ISS (n=10) and GHD (n=17) who had normal pretreatment IGFISDS. An untreated group of children with ISS (n=12) served as a control group.

RESULTS

At presentation, the height standard deviation score (HtSDS) of children with ISS who had low pretreatment IGFISDS was significantly lower compared to the normal IGFI group. The age, body mass index (BMI), BMISDS, peak GH response to clonidine provocation and bone age did not differ between the two study groups. After 1 year of treatment with rhGH (0.035-0.06 mg/kg/day) IGFISDS increased significantly in both groups (p<0.05). Both had significantly increased HtSDS (catch-up growth). The increase in the HtSDS and WGPD were significantly greater in the lower pretreatment IGFISDS group. The IGFSDS, BMISDS, HtSDS and difference between HtSDS and mid-parental HtSDS were significantly greater in the rhGH treated groups vs. the not treated group. In the GHD groups (normal and low IGFISDS), after 1 year of GH therapy (0.03-0.05 mg/kg/day), the HtSDS increased significantly in both, (p<0.01). The WGPD and increment in BMI were significantly greater in children who had low pretreatment IGFISDS. There was a significant increase in the IGFSDS in the two treated groups (p<0.05), however, the WGPD was greater in the pretreatment low IGFISDS.

CONCLUSIONS

IGFI deficiency represents a low anabolic state. Correction of IGFI level (through rhGH and/or improved nutrition) in short children (ISS and GHD) was associated with increased linear growth and WGPD denoting significant effect on bone growth and muscle protein accretion.

Impact of oral nutritional supplements (ONS) on growth outcomes and IGF-1 level in underweight older children and young adolescents (5-14 years) with short stature and no systemic disease: High versus normal calories density formula

Objectives:

This controlled trial investigated the effects of energy-dense pediatric oral nutritional supplements ONS versus standard ONS in pediatric patients requiring oral nutritional support for low body mass index (BMI) or weight gain per day (WGD) below the average for age and sex.

Patients and Methods:

34 children and adolescents (mean age 10.2 years) with faltering growth requiring ONS were randomized to cONS (n =22) or sONS (n = 12) for a year. We recorded their weight (WT), height (HT) and calculated height growth velocity (GV), Ht-SDS, BMI, WGD, every 3 months for a year.

Results:

The WGD, height growth velocity (GV: cm/year), and Ht-SDS increased significantly, in both groups, during the year of ONS. The use of the cONS resulted in significantly greater mean total WGD and BMI-SDS after 6 months and 1 year, compared to the sONS group. The increase in IGF1-SDS was significantly higher in the cONS groups versus the sONS group. Moreover, the WGD was correlated significantly with the height GV during the year of ONS intake.

Conclusions:

ONS improved the growth of underweight old children and adolescents who had no systemic illness. There was a significantly higher WGD and BMI-SDS in the group on cONS compared to those on sONS. In both groups, long-term use of ONS significantly improved Ht-SDS. (www.actabiomedica.it)

Defining age- and lactocrine-sensitive elements of the neonatal porcine uterine microRNA-mRNA interactome

Factors delivered to offspring in colostrum within 2 days of birth support neonatal porcine uterine development. The uterine mRNA transcriptome is affected by age and nursing during this period. Whether uterine microRNA (miRNA) expression is affected similarly is unknown. Objectives were to (1) determine effects of age and nursing on porcine uterine miRNA expression between birth and postnatal day (PND) 2 using miRNA sequencing (miRNAseq) and; (2) define affected miRNA–mRNA interactions and associated biological processes using integrated target prediction analysis. At birth (PND 0), gilts were euthanized, nursed ad libitum, or gavage-fed milk replacer for 48 h. Uteri were collected at birth or 50 h postnatal. MicroRNAseq data were validated using quantitative real-time PCR. Targets were predicted using an established mRNA database generated from the same tissues. For PND 2 versus PND 0 comparisons, 31 differentially expressed (DE) miRNAs were identified for nursed, and 42 DE miRNAs were identified for replacer-fed gilts. Six DE miRNAs were identified for nursed versus replacer-fed gilts on PND 2. Target prediction for inversely correlated DE miRNA–mRNA pairings indicated 20 miRNAs targeting 251 mRNAs in nursed, versus 29 miRNAs targeting 585 mRNAs in replacer-fed gilts for PND 2 versus PND 0 comparisons, and 5 miRNAs targeting 81 mRNAs for nursed versus replacer-fed gilts on PND 2. Biological processes predicted to be affected by age and nursing included cell-to-cell signaling, cell morphology, and tissue morphology. Results indicate novel age- and lactocrine-sensitive miRNA–mRNA relationships associated with porcine neonatal uterine development between birth and PND 2.

Effects of colostrum, feeding method and oral IGF1 on porcine uterine development

Nursing ensures lactocrine delivery of maternally derived, milk-borne bioactive factors to offspring, which affects postnatal development of female reproductive tract tissues. Disruption of lactocrine communication for two days from birth (postnatal day (PND) 0) by feeding milk replacer in lieu of nursing or consumption of colostrum alters porcine uterine gene expression globally by PND 2 and inhibits uterine gland genesis by PND 14. Here, objectives were to determine effects of: (1) nursing or milk replacer feeding from birth; (2) a single dose of colostrum or milk replacer and method of feeding and (3) a single feeding of colostrum or milk replacer, with or without oral supplementation of IGF1, administered at birth on aspects of porcine uterine development at 12-h postnatally. Results indicate nursing for 12 h from birth supports rapid establishment of a uterine developmental program, illustrated by patterns of endometrial cell proliferation, expression of genes associated with uterine wall development and entry into mitosis and establishment of a uterine MMP9/TIMP1 system. A single feeding of colostrum at birth increased endometrial cell proliferation at 12 h, regardless of method of feeding. Oral supplementation of IGF1 was sufficient to support endometrial cell proliferation at 12 h in replacer-fed gilts, and supplementation of colostrum with IGF1 further increased endometrial cell proliferation. Results indicate that lactocrine regulation of postnatal uterine development is initiated with the first ingestion of colostrum. Further, results suggest IGF1 may be lactocrine-active and support a 12-h bioassay, which can be used to identify uterotrophic lactocrine activity.

Maternal lactocrine programming of porcine reproductive tract development

The lactocrine hypothesis for maternal programming of female reproductive tract development is based on the idea that non-nutritive, milk-borne bioactive factors (MbFs), delivered from mother to offspring during nursing, play a role in determining the trajectory of development with long-term consequences in the adult. Porcine female reproductive tract development is completed postnatally, and the period during which maternal support of neonatal growth derives exclusively from colostrum/milk defines a window of opportunity for lactocrine programming of reproductive tissues. Beyond nutrition, milk serves as a delivery system for a variety of bioactive factors. Porcine relaxin is a prototypical MbF. Present in colostrum at highest concentrations at birth, relaxin is transmitted into the circulation of nursing piglets where it can act on Relaxin receptors found in neonatal female reproductive tract tissues. This process is facilitated by the physiology of the maternal-neonatal dyad and the fact that the neonatal gastrointestinal tract is open to absorb macromolecules for a period of time postnatally. Age at first nursing and duration of nursing from birth are also important for porcine female reproductive tract development. These parameters affect both the quality and quantity of colostrum consumed. Disruption of lactocrine signaling by feeding milk replacer from birth altered porcine uterine, cervical, and testicular development by postnatal Day 2. Moreover, insufficient colostrum consumption in nursing piglets can impair uterine capacity to support viable litters of optimal size in adulthood. In the pig, lactocrine signaling supports neonatal organizational events associated with normal reproductive development and may program adult uterine capacity.

Age and Nursing Affect the Neonatal Porcine Uterine Transcriptome

The lactocrine hypothesis for maternal programming of neonatal development was proposed to describe a mechanism through which milk-borne bioactive factors, delivered from mother to nursing offspring, could affect development of tissues, including the uterus. Porcine uterine development, initiated before birth, is completed postnatally. However, age- and lactocrine-sensitive elements of the neonatal porcine uterine developmental program are undefined. Here, effects of age and nursing on the uterine transcriptome for 48 h from birth (Postnatal Day [PND] = 0) were identified using RNA sequencing (RNAseq). Uterine tissues were obtained from neonatal gilts (n = 4 per group) within 1 h of birth and before feeding (PND 0), or 48 h after nursing ad libitum (PND 2N) or feeding a commercial milk replacer (PND 2R). RNAseq analysis revealed differentially expressed genes (DEGs) associated with both age (PND 2N vs. PND 0; 3283 DEGs) and nursing on PND 2 (PND 2N vs PND 2R; 896 DEGs). Expression of selected uterine genes was validated using quantitative real-time PCR. Bioinformatic analyses revealed multiple biological processes enriched in response to both age and nursing, including cell adhesion, morphogenesis, and cell-cell signaling. Age-sensitive pathways also included estrogen receptor-alpha and hedgehog signaling cascades. Lactocrine-sensitive processes in nursed gilts included those involved in response to wounding, the plasminogen activator network and coagulation. Overall, RNAseq analysis revealed comprehensive age- and nursing-related transcriptomic differences in the neonatal porcine uterus and identified novel pathways and biological processes regulating uterine development.

Human β-defensin-3 promotes intestinal epithelial cell migration and reduces the development of necrotizing enterocolitis in a neonatal rat model

BACKGROUND

The aim of this study was to investigate the effects of human β-defensin-3 (hBD3) on intestinal wound healing and in a neonatal rat model of necrotizing enterocolitis (NEC).

METHODS

Enterocyte migration and proliferation were detected in vitro and in vivo. The role of chemokine receptor CCR6 and its downstream signaling pathway was assessed. Newborn Sprague-Dawley rats were randomly divided into four groups: Control+NS, Control+hBD3, NEC+NS, and NEC+hBD3. Body weight, histological score, survival time, cytokines expression, and mucosal integrity were evaluated.

RESULTS

hBD3 could stimulate enterocyte migration, but not proliferation, both in cultured enterocytes and in the NEC model. Neutralizing antibody and small interfering RNA confirmed this stimulatory effect was mediated by CCR6. Furthermore, hBD3 induced Rho activation, myosin light chain 2 phosphorylation, and F-actin accumulation. The bactericidal activity of hBD3 was maintained throughout a broad pH range. Strikingly, hBD3 administration decreased the incidence of NEC, increased the survival rate, and reduced the severity of NEC. Moreover, hBD3 reduced the proinflammatory cytokines expression in ileum and serum and preserved the intestinal barrier integrity.

CONCLUSION

This study provided evidence that the antimicrobial peptide hBD3 might participate in intestinal wound healing by promoting enterocyte migration and show beneficial effects on newborn rats with NEC.

Effects of age, nursing, and oral IGF1 supplementation on neonatal porcine cervical development

Nursing supports neonatal porcine uterine and testicular development, however, lactocrine effects on cervical development are undefined. Studies were conducted to determine the effects of i) age and the imposition of the lactocrine-null state from birth (postnatal day 0 (PND0)) by milk replacer feeding on cervical histology; ii) imposition of the lactocrine-null state for 2 days from birth on cervical cell proliferation, as reflected by proliferating cell nuclear antigen immunostaining; and iii) a single feeding of colostrum or milk replacer, administered at birth, with or without oral IGF1, on cervical cell proliferation and phosphorylated AKT (pAKT) and B-cell lymphoma 2 (BCL2) protein levels at 12 h postnatal. Cervical crypt depth and height of luminal epithelium (LE) increased with age by PND14, when both responses were reduced in replacer-fed gilts. Cell proliferation was reduced in LE at PND2, and in crypt epithelium and stroma by PND14 in replacer-fed gilts. Returning replacer-fed gilts to nursing on PND2 did not rescue the cervical phenotype by PND14. A single feeding of colostrum, but not milk replacer, was sufficient to support cervical cell proliferation at 12 h postnatal. IGF1 supplementation induced cell proliferation in replacer-fed gilts, and increased cervical pAKT and BCL2 levels in colostrum-fed gilts and replacer-fed gilts at 12 h postnatal. Results indicate that age and nursing support porcine cervical development, support is initiated at first ingestion of colostrum, IGF1 may be lactocrine-active, and identification of lactocrine-active factors can be accomplished by 12 h postnatal using this bioassay system.

Nursing during the first two days of life is essential for the expression of proteins important for growth and remodeling of the neonatal porcine cervix

The neonatal porcine cervix is sensitive to hormones, including relaxin (RLX), from birth. Whether nursing is required to establish the cervical developmental program or to determine cervical developmental trajectory is unknown. The objective of study 1 was to determine effects of age and nursing on expression of molecular markers and mediators of porcine cervical growth and remodeling from birth to postnatal day (PND) 2 and to document effects of RLX treatment during this period on expression of targeted gene products in nursed vs. replacer-fed gilts. Study 2 was conducted to determine effects of age at first nursing and duration of nursing from birth on expression of targeted transcripts or proteins at PND 14. Nursing supported cervical estrogen receptor-α, vascular endothelial growth factor, matrix metalloproteinase (MMP)9, and antiapoptotic B-cell lymphoma-2 protein expression on PND 2. These proteins were undetectable in replacer-fed gilts. Returning replacer-fed gilts to nursing after PND 2 did not restore cervical expression of these proteins by PND 14. RLX increased (P < 0.05) cervical estrogen receptor-α, vascular endothelial growth factor, and B-cell lymphoma-2 protein in nursed gilts, MMP2 protein in nursed and replacer-fed gilts, and decreased (P < 0.05) pro-MMP9 protein in nursed gilts, and RXFP1 mRNA levels in nursed and replacer-fed gilts at PND 2. Replacer feeding for 2 wk from birth increased (P < 0.05) RXFP1 mRNA levels on PND 14. Results support the lactocrine hypothesis for maternal programming of neonatal tissues. Nursing from birth is required to establish the neonatal cervical developmental program and to maintain cervical developmental trajectory to PND 14.

Interferon-gamma inhibits enterocyte migration by reversibly displacing connexin43 from lipid rafts

Necrotizing enterocolitis (NEC) is associated with the release of interferon-gamma (IFN) by enterocytes and delayed intestinal restitution. Our laboratory has recently demonstrated that IFN inhibits enterocyte migration by impairing enterocyte gap junctions, intercellular channels that are composed of connexin43 (Cx43) monomers and that are required for enterocyte migration to occur. The mechanisms by which IFN inhibits gap junctions are incompletely understood. Lipid rafts are cholesterol-sphingolipid-rich microdomains of the plasma membrane that play a central role in the trafficking and signaling of various proteins. We now hypothesize that Cx43 is present on enterocyte lipid rafts and that IFN inhibits enterocyte migration by displacing Cx43 from lipid rafts in enterocytes. We now confirm our previous observations that intestinal restitution is impaired in NEC and demonstrate that Cx43 is present on lipid rafts in IEC-6 enterocytes. We show that lipid rafts are required for enterocyte migration, that IFN displaces Cx43 from lipid rafts, and that the phorbol ester phorbol 12-myristate 13-acetate (PMA) restores Cx43 to lipid rafts after treatment with IFN in a protein kinase C-dependent manner. IFN also reversibly decreased the phosphorylation of Cx43 on lipid rafts, which was restored by PMA. Strikingly, restoration of Cx43 to lipid rafts by PMA or by transfection of enterocytes with adenoviruses expressing wild-type Cx43 but not mutant Cx43 is associated with the restoration of enterocyte migration after IFN treatment. Taken together, these findings suggest an important role for lipid raft-Cx43 interactions in the regulation of enterocyte migration during exposure to IFN, such as NEC.

Temporal changes in insulin-like growth factors I and II and in insulin-like growth factor binding proteins 1, 2, and 3 in human milk

AIM

To evaluate the postpartum time course of changes in insulin-like growth factors (IGFs) and their binding proteins (IGFBPs).

METHODS

Breast milk IGF-I and IGF-II and IGFBP-1, IGFBP-2, and IGFBP-3 levels were determined in 23 women with babies born at term, from day 4 until up to 9 months after birth.

RESULTS

The IGFBP-3 levels were highest from day 4 to day 6 and then decreased by days 10-12. In contrast, IGF-I and IGF-II and IGFBP-1 and IGFBP-2 showed little change over the first 2 weeks after birth. Subsequently, all the IGF components showed a moderate decline over approximately the first 1-3 months and then stable levels up to 9 months after birth.

CONCLUSION

Although the possibility cannot be excluded that these changes in levels of IGFs and their binding proteins in human milk represent passive loss from the mammary gland, we speculate that higher early levels of the human milk IGF system contribute to maturation of the infant gut.

Insulin-like growth factors (IGFs), IGF binding proteins, and other endocrine factors in milk: role in the newborn

The role of colostrum and milk in the neonate has been chiefly recognized as a comprehensive nutrient foodstuff. In addition, the provision of colostrum-the first milk-for early immune capacity has been well documented for several species. Colostrum is additionally a rich and concentrated source of various factors that demonstrate biological activity in vitro. Three hypotheses have been proposed for the phenotypic function of these secreted bioactive components: (1) only mammary disposal, (2) mammary cell regulation, and (3) neonatal function [gastrointestinal tract (GIT) or systemic]. Traditionally, it was assumed that the development of the GIT is preprogrammed and not influenced by events occurring in the intestinal lumen. However, a large volume of research has demonstrated that colostrum (or milk-borne) bioactive components can basically contribute to the regulation of GIT growth and differentiation, while their role in postnatal development at physiological concentrations has remained elusive. Much of our current understanding is derived from cell culture and laboratory animals, but experimentation with agriculturally important species is taking place. This chapter provides an overview of work conducted primarily in neonatal calves and secondarily in other species on the effects on neonates of selected peptide endocrine factors (hormones, growth factors, in part cytokines) in colostrum. The primary focus will be on insulin-like growth factors (IGFs) and IGF binding proteins (IGFBPs) and other bioactive peptides, but new interest and concern about steroids (especially estrogens) in milk are considered as well.

Development of the infant intestine: implications for nutrition support

The incidence of preterm births has continued to increase over the past 25 years, and therefore the optimal feeding of these infants is an important clinical concern. This review focuses on intestinal development and physiology, with a particular emphasis on developmentally immature functions of the preterm intestine and the resulting implications for nutrition therapies used to feed the preterm infant.

Nitric oxide inhibits enterocyte migration through activation of RhoA-GTPase in a SHP-2-dependent manner

Diseases of intestinal inflammation like necrotizing enterocolitis (NEC) are associated with impaired epithelial barrier integrity and the sustained release of intestinal nitric oxide (NO). NO modifies the cytoskeletal regulator RhoA-GTPase, suggesting that NO could affect barrier healing by inhibiting intestinal restitution. We now hypothesize that NO inhibits enterocyte migration through RhoA-GTPase and sought to determine the pathways involved. The induction of NEC was associated with increased enterocyte NO release and impaired migration of bromodeoxyuridine-labeled enterocytes from terminal ileal crypts to villus tips. In IEC-6 enterocytes, NO significantly inhibited enterocyte migration and activated RhoA-GTPase while increasing the formation of stress fibers. In parallel, exposure of IEC-6 cells to NO increased the phosphorylation of focal adhesion kinase (pFAK) and caused a striking increase in cell-matrix adhesiveness, suggesting a mechanism by which NO could impair enterocyte migration. NEC was associated with increased expression of pFAK in the terminal ileal mucosa of wild-type mice and a corresponding increase in disease severity compared with inducible NO synthase knockout mice, confirming the dependence of NO for FAK phosphorylation in vivo and its role in the pathogenesis of NEC. Strikingly, inhibition of the protein tyrosine phosphatase SHP-2 in IEC-6 cells prevented the activation of RhoA by NO, restored focal adhesions, and reversed the inhibitory effects of NO on enterocyte migration. These data indicate that NO impairs mucosal healing by inhibiting enterocyte migration through activation of RhoA in a SHP-2-dependent manner and support a possible role for SHP-2 as a therapeutic target in diseases of intestinal inflammation like NEC.

Heparin-binding epidermal growth factor-like growth factor promotes enterocyte migration and proliferation in neonatal rats with necrotizing enterocolitis

PURPOSE

We have shown that heparin-binding epidermal growth factor-like growth factor (HB-EGF) decreases experimental necrotizing enterocolitis (NEC). Intestinal epithelial cell (IEC) migration (restitution) and proliferation are key elements in recovery from intestinal injury. Here, we investigated whether the beneficial effects of HB-EGF are mediated, in part, by its ability to affect these processes.

METHODS

Necrotizing enterocolitis was induced in newborn rats by exposure to stress (hypoxia, hypothermia, hypertonic feedings, and lipopolysaccharide), with pups receiving different doses of HB-EGF (0, 25, 50, 100, 200, 400, 600, and 800 microg/kg). To investigate the effect of HB-EGF on enterocyte proliferation and migration, bromodeoxyuridine was administered intraperitoneally 18 hours before sacrifice, with intestine subjected to bromodeoxy-uridine immunohistochemistry.

RESULTS

The incidence and severity of experimental NEC decreased, and the survival rate increased, with increasing doses of HB-EGF. Results were confirmed using scanning electron microscopy. Migration of IEC in breast-fed pups was 7.07 microm/h, decreased significantly to 2.29 microm/h in stressed pups, and was significantly improved at 5.95 microm/h in pups subjected to stress but treated with HB-EGF (P < .05). Quantification of IEC proliferation revealed 208 (+) cells per high-power field (HPF) in breast-fed pups, which decreased significantly to 99 (+) cells per HPF in stressed pups and increased to 190 (+) cells per HPF in stressed pups treated with HB-EGF (P < .05).

CONCLUSIONS

These results demonstrate that HB-EGF protects newborn rats from experimental NEC in a dose-dependent fashion. The ability of HB-EGF to protect the intestines from NEC is due, in part, to the ability of HB-EGF to preserve enterocyte migration and proliferation.

Effects of Oral Administration of Insulin-Like Growth Factor-I on Circulating Concentration of Insulin-Like Growth Factor-I and Growth of Internal Organs in Weanling Mice

Insulin-like growth factor (IGF)-I is a polypeptide that mediates the growth-promoting action of growth hormone in postnatal animals. The present study was conducted to examine whether orally administered IGF-I would be absorbed into the general circulation and also whether ingested IGF-I would enhance the growth of whole body as well as internal organs, and tissues in 3-week-old ICR-strain female weanling mice. In experiment (Exp) 1, a total of 70 mice received IGF-I orally at 1 microg.g-1 in 0.2-ml PBS or the vehicle alone. Concentrations of IGF-I and glucose in heart blood were measured after killing 5 animals in each group every fourth hour during a 24-hour period. In Exp 2, a total of 40 mice received oral IGF-I administration at 1 microg.g-1 or vehicle every third day beginning from day 0 for a 13-day period. Half the animals were killed at day 7 and the other half at day 13. Weights of whole body and organs/tissues (small intestine, liver, thigh muscle, and brain) were measured every day and at slaughter, respectively. In Exp 1, following the oral IGF-I administration, serum IGF-I concentration increased at hour 4 (p<0.01) and returned to the hour 0 level by hour 8, whereas glucose concentration was lowest at hour 4 and returned to the hour 0 level by hour 16. In the PBS-fed group, neither IGF-I nor glucose concentration changed during the 24-hour period. In Exp 2, weight of small intestine increased (p<0.05) in response to the oral IGF-I, whereas weights of liver and thigh muscle of the IGF-I-fed group were greater (p<0.01) and tended to be greater (p=0.06), respectively, than those of the PBS-fed only at day 13. However, brain weight and serum concentrations of IGF-I and IGF-II were not affected by oral IGF-I administration. Results suggest that although orally administered IGF-I mainly acts at the intestine, a portion of ingested IGF-I is absorbed into the general circulation to enhance the growth of selective organs/tissues in weanling mice.

Dietary insulin affects leucine aminopeptidase, growth hormone, insulin-like growth factor I and insulin receptors in the intestinal mucosa of neonatal pigs

BACKGROUND

Recent studies suggest that milk-borne insulin may regulate the development of the gastrointestinal tract in neonatal mammals.

OBJECTIVES

To explore the mechanism by which milk-borne insulin affects gastrointestinal tract development, we examined the effect of dietary insulin on the expression levels of leucine aminopeptidase (LAP) and insulin-like growth factor I (IGF-I), as well as its effect on growth hormone (GH), IGF-I and insulin receptors in the small intestinal mucosa of neonatal pigs.

METHODS

Five piglets were anesthetized and sampled within 2-4 h after birth. They were not allowed to suckle and were used as newborn controls (group N). Ten other piglets from 5 litters were randomly divided into group M (n=5), which was fed cow's milk, and group MI (n=5), which was fed cow's milk and insulin (2.5 mg/l). Piglets in groups M and MI were artificially fed for 3 days and then sampled. Total RNA in their intestinal mucosa was extracted with Tripure reagents (Roche, USA). Reverse transcription PCR (RT-PCR) was used to semi-quantify mRNA levels of target genes and 18S rRNA was used in an RT-PCR system as an internal control. PCR products were loaded onto a 9% nondenaturing polyacrylamide gel. The gel was stained by silver staining agents. Digital photos were taken and the strength of the band areas was quantified using software.

RESULTS

The results showed that the DNA contents and LAP activity in the small intestines of the piglets in group MI were higher (p<0.05) than in the piglets in group N. Compared with group M, piglets in group MI exhibited significantly increased expression levels of both insulin and GH receptor in the ileum, and LAP in the jejunum (p<0.05); IGF-I receptor expression levels in both the jejunum and ileum were significantly decreased (p<0.01 and p<0.05, respectively), while IGF-I expression was unchanged (p>0.05).

CONCLUSION

Collectively, dietary insulin increased mRNA levels of insulin and GH receptor, which could help explain the effect of dietary insulin on receptor-mediated postnatal development of the small intestine. Dietary insulin suppressed IGF-I receptor expression, which may be the result of negative feedback caused when insulin binds to IGF-I receptors.

Nutritional physiology of neonatal calves*

The gastrointestinal tract of neonatal calves is relatively mature but still requires morphological and functional changes. The intake of colostrum with its nutrient and non-nutrient components exerts marked effects on gastrointestinal development and function. Colostrum intake provides immunoprotection (passive immunity by immunoglobulins) and is essential for survival of neonates of most species. Furthermore, there are important transient as well as long-lasting systemic effects on the nutritional status, on metabolism, and on various endocrine systems due to intake of nutrient and non-nutrient colostral components that contribute to survival in the stressful postnatal period. Colostrum is much more than just a supplier of immunoglobulins.

Effect of a short-term fast on intestinal disaccharidase activity and villus morphology of piglets suckling insulin-like growth factor-I transgenic sows1

The objectives of this study were to use transgenic sows that overexpress IGF-I in milk to investigate the effect of a short-term fast on piglet intestinal morphology and disaccharidase activity and to determine how milk-borne IGF-I influences the response to fasting. After farrowing, litters were normalized to 10 piglets. On d 6, piglets (n = 30) suckling IGF-I transgenic (TG) sows and piglets (n = 30) suckling nontransgenic sows (control) were assigned randomly to three treatments: fed piglets (0 h), which remained with the sow until euthanized on d 7, or fasted piglets, which were removed from the sow at either 6 or 12 h before euthanasia on d 7. Serum IGF-I and IGFBP, intestinal weight and length, jejunal protein and DNA content, disaccharidase activity, and villus morphology were measured. Fasting for 12 h resulted in a negative weight change between d 6 and 7 (quadratic response to fasting; P < 0.001). Piglets suckling TG sows tended to have greater intestinal length (P = 0.068), but no effect of IGF-I overexpression was noted for intestinal weight. Fasting, however, resulted in linear (P < 0.001) and quadratic (P = 0.002) decreases in intestinal weight. Serum IGF-I did not differ between control and TG sows, but decreased linearly (P = 0.003) with fasting. Serum IGFBP-4 decreased (linear and quadratic; P < or = 0.02) with fasting, whereas IGFBP-1 increased quadratically (P < 0.001) with fasting. Jejunal villus height, width, and crypt depth were all increased with fasting (linear and quadratic; P < 0.04). Disaccharidase activity was not affected by fed state; however, piglets suckling TG sows had greater jejunal lactase-phlorhizin hydrolase (P < 0.01) and sucrase-isomaltase (P = 0.02) activities than control piglets. In summary, intestinal weight, villus morphology, serum IGF-I, serum IGFBP-1 and -4, and piglet BW change were altered (P < or = 0.02) in response to fasting. Thus, the duration of food deprivation before euthanization should be considered when designing experiments to assess intestinal development or the IGF axis, as the magnitude of differences between the fed and fasted state may exceed those expected as a result of experimental treatment.

Mammary Specific Transgenic Over-expression of Insulin-like Growth Factor-I (IGF-I) Increases Pig Milk IGF-I and IGF Binding Proteins, with no Effect on Milk Composition or Yield

IGF-I regulates lactation by stimulating mammary mitogenesis, inhibiting apoptosis, and partially mediating the effects of growth hormone on lactogenesis. Herein, lactation performance during first and second parity was assessed in transgenic swine (TG) that over-expressed human IGF-I in milk under the control of the bovine alpha-lactalbumin promoter, regulatory regions and signal peptide coding sequence. Milk samples were collected throughout lactation (farrowing to d24) from TG sows and non-transgenic littermates (CON) and IGF-I, IGF-II, and IGFBP determined. Colostral (<24 h postpartum) IGF-I content was 26-fold greater (p<0.001) in TG sows (949+/- 107 microg/L; range 228-1,600 microg/L) than CON (36+/-17.8 microg/L) and was 50- to 90-fold greater (p< 0.001) in mature milk (d2-24 postpartum). There was no effect of parity on milk IGF-I content. Milk IGF-II concentration was unaffected by IGF-I over-expression. Low molecular weight IGFBP (IGFBP-2 and -5) in the milk of TG sows were higher (p=0.02) than CON in the early postpartum period, but did not differ in mature milk. Milk yield, determined by weigh-suckle-weigh, was similar in TG and CON as was litter weight gain. Milk nutrient composition was not significantly affected by IGF over-expression. Thus, mammary specific transgenic over-expression of IGF-I significantly increased milk IGF-I and IGFBP content, but did not impact lactation performance in swine.

Increased expression and function of integrins in enterocytes by endotoxin impairs epithelial restitution

BACKGROUND & AIMS

Experimental necrotizing enterocolitis (NEC) is characterized by circulating endotoxin (lipopolysaccharide [LPS]) and impaired enterocyte migration. We hypothesized that LPS increases integrin function and cell-matrix adhesion, leading to impaired enterocyte migration in the pathogenesis of NEC.

METHODS

NEC-like intestinal injury was induced in newborn rats by hypoxia/gavage feedings, and restitution was determined by assessing bromodeoxyuridine-labeled enterocytes along the crypt-villus axis. Newborn mice were injected with 5 mg/kg LPS. IEC-6 cells were treated with LPS +/- LY294002 or wortmannin, and beta 1- and alpha 3-integrins were assessed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and immunofluorescence. Beta 1-integrin function was determined by adherence of fibronectin beads to IEC-6 monolayers. Migration of IEC-6 cells into a scraped wound was measured by time-lapse microscopy.

RESULTS

Newborn intestinal injury was associated with decreased intestinal restitution and increased alpha 3- and beta 1-integrin expression in the ileal mucosa, which also was observed after LPS injection. In IEC-6 cells, LPS caused an increase in the expression of alpha 3- and beta 1-integrins, a shift of beta 1-integrins from the cytoplasm to the plasma membrane and an increase in fibronectin bead adhesion during which beta 1-integrins accumulated underneath attached beads. These effects could be reversed with LY294002 or wortmannin, suggesting phosphatidylinositol-3-phosphate kinase (PI3K) dependence. The increased integrin-matrix adhesion by LPS led to an inhibition of enterocyte migration, which could be reversed by anti-beta 1-antibodies.

CONCLUSIONS

Enterocyte migration is inhibited by LPS through increased expression and function of alpha 3- and beta 1-integrins. Modulation of enterocyte migration via integrins may provide novel insights into the pathogenesis of NEC, in which intestinal restitution is impaired.

Genistein inhibits intestinal cell proliferation in piglets

Currently 15% of U.S. infants are fed soy formulas that contain up to 14 mg of genistein equivalents/L. Our goal was to investigate the impact of dietary genistein on intestinal development. Piglets (n=8/group) were fed sow milk replacer (MR), MR+1 mg/L of genistein (LG), or MR+14 mg/L of genistein (HG) for 10 d. Formula intake, weight gain, and intestinal length and weight were similar in all groups. Average serum genistein concentration in the HG group was similar to that of soy formula-fed infants. No significant effects of genistein on enterocyte apoptosis, lactase, and sucrase activities or electrophysiologic measures were observed in jejunum or ileum. Jejunal and ileal villus heights were not significantly different, but the percentage of proliferating cell nuclear antigen-positive jejunal crypt cells in the HG was reduced 50% compared with that in MR and LG (p=0.001), indicating decreased proliferation. Enterocyte migration distance in the HG group tended to be 20% less (p=0.1) than LG or MR. Jejunal estrogen receptor beta mRNA expression in HG was half of that in LG (p=0.05), but neither was significantly different from MR. In conclusion, genistein at the level present in soy infant formula is bioactive in the small intestine and results in reduced enterocyte proliferation and migration. The lack of effect of genistein on nutrient transport and enzyme activity suggests that the impact of genistein is greater on proliferating versus differentiated intestinal cells.

Effects of enterally administering granulocyte colony-stimulating factor to suckling mice

Gastrointestinal (GI) tract development is influenced by multiple growth factors, some of which are delivered directly to the GI lumen, as they are swallowed constituents of amniotic fluid, colostrum, and milk. Granulocyte colony-stimulating factor (G-CSF), traditionally known as a granulocytopoietic growth factor, is an example of one such factor. However, it is not clear whether the large amounts of G-CSF that are normally swallowed by the fetus and neonate have systemic effects on circulating neutrophils or local effects in the developing intestine. To assess this, we administered either active or heat-denatured (control) recombinant human G-CSF to 5- to 7-d-old C57BL/6 x 129SvJ mice. Pups received either a low dose (3 ng) that was calculated to approximate the amount of G-CSF swallowed in utero from amniotic fluid or an isovolemic high dose 100 times larger (300 ng). Oral dosing was performed daily for either 3 or 7 d, after which pups were killed and measurements were made on the blood and the GI tract. Absolute blood neutrophil counts and immature to total neutrophil ratios did not differ from controls in any of the test groups. However, intestinal villus area, perimeter, length, crypt depth, and proliferating cell nuclear antigen index increased significantly among those that were treated with active G-CSF. Thus, in suckling mice, enterally administered G-CSF had no effect on the concentration of circulating neutrophils but had trophic effects on the intestine. We speculate that the G-CSF present in amniotic fluid, colostrum, and milk acts as a topical intestinal growth factor and has little or no granulocytopoietic action.

Endotoxin inhibits intestinal epithelial restitution through activation of Rho-GTPase and increased focal adhesions

Diseases of gut inflammation such as neonatal necrotizing enterocolitis (NEC) result after an injury to the mucosal lining of the intestine, leading to translocation of bacteria and endotoxin (lipopolysaccharide). Intestinal mucosal defects are repaired by the process of intestinal restitution, during which enterocytes migrate from healthy areas to sites of injury. In an animal model of NEC, we determined that intestinal restitution was significantly impaired compared with control animals. We therefore sought to determine the mechanisms governing enterocyte migration under basal conditions and after an endotoxin challenge. Here we show that the cytoskeletal reorganization and stress fiber formation required for migration in IEC-6 enterocytes requires RhoA. Enterocytes were found to express the endotoxin receptor Toll-like receptor 4, which served to bind and internalize lipopolysaccharide. Strikingly, endotoxin treatment significantly inhibited intestinal restitution, as measured by impaired IEC-6 cell migration across a scraped wound. Lipopolysaccharide was found to increase RhoA activity in a phosphatidylinositol 3-kinase-dependent manner, leading to an increase in phosphorylation of focal adhesion kinase and an enhanced number of focal adhesions. Importantly, endotoxin caused a progressive, RhoA-dependent increase in cell matrix tension/contractility, which correlated with the observed impairment in enterocyte migration. We therefore conclude that endotoxin inhibits enterocyte migration through a RhoA-dependent increase in focal adhesions and enhanced cell adhesiveness, which may participate in the impaired restitution observed in experimental NEC.

IGF-I augments resection-induced mucosal hyperplasia by altering enterocyte kinetics

Our objective was to determine if exogenous insulin-like growth factor-I (IGF-I) augments the adaptive growth response to mid small bowel resection in association with changes in enterocyte kinetics. We determined structural adaptation and concomitant changes in enterocyte proliferation, apoptosis, and migration of the jejunum in growing, parenterally fed rats after mid small bowel resection or small bowel transection, and treatment with IGF-I or vehicle. IGF-I treatment in resected rats significantly increased jejunal mucosal mass by 20% and mucosal concentrations of protein and DNA by 36 and 33%, respectively, above the response to resection alone. The enhancement of resection-induced adaptive growth and cellularity by IGF-I reflected an increase in enterocyte proliferation, an expansion of the proliferative compartment in the crypt, and no further decrease in enterocyte apoptosis or increase in enterocyte migration beyond the effects of resection. The ability of IGF-I to augment the mucosal hyperplasia stimulated by the endogenous response to resection substantiates the role of IGF-I as an intestinal mitogen that promotes tissue regeneration.

IGF alters jejunal glucose transporter expression and serum glucose levels in immature rats

Milk-borne insulin-like growth factors (IGFs) enhance nutrient absorption in the immature intestine, which is characterized by low levels of glucose oxidation. We therefore hypothesized that feeding a rat milk substitute (RMS) devoid of growth factors to rat pups would lower serum glucose levels relative to dam-fed control rats and that supplementation of RMS with physiological doses of either IGF-I or IGF-II would normalize serum glucose levels via increased jejunal glucose transporter 2 (GLUT2) and high-affinity Na(+)-glucose cotransporter (SGLT1) expression. We found lower serum glucose concentrations in RMS-fed pups; in contrast, serum glucose levels in the IGF-supplemented pups were similar to those of dam-fed controls. RT-PCR and laser scanning confocal microscopy similarly demonstrated that IGF supplementation increased expression of jejunal glucose transporters. Further experiments demonstrated that IGF supplementation altered mRNA levels of key mitochondrial enzymes without altering jejunal lactase activity. We conclude that IGF-I and IGF-II supplementation increases serum glucose levels in the immature rat pup fed artificial formula and alters gene expression of the jejunal glucose transporters.

Key nutrients and growth factors for the neonatal gastrointestinal tract

The nutritional support of gastrointestinal growth and function is an important consideration in the clinical care of neonatal infants. In most health infants, the provision of either breast milk or formula seems to support normal intestinal mucosal growth, but the most significant advantages of breast milk may be for host defense or gut barrier-related functions that are involved in reducing infection. The specific effects of various milk-borne growth factors on key mucosal immune and barrier functions are likely to provide valuable new clues to the advantages of human milk. A substantial number of preterm, low-birth weight babies or those suffering from compromised intestinal function, however, often cannot tolerate oral feedings and instead receive TPN. The consequences of TPN on gastrointestinal function and how this contributes to morbidity of these infants warrants further study, with respect to both clinical and basic research questions. Although enteral nutrition seems to be a critical stimulus for intestinal function, the minimal amounts and composition of nutrients necessary to maintain specific intestinal functions remain to be established. The experimental tools exist to start defining the specific nutrient requirements for the infant gut and some of these nutrients are known (e.g., glutamate, glutamine, and threonine). Peptide growth factors and gut hormones clearly play a role in gut growth and in several ways mediate the trophic actions of enteral nutrition. Although a number of these growth factors are good candidates for therapeutic use, their clinical application in the management of gastrointestinal insufficiency and disease has been slow. The emergence of GLP-2 as a trophic peptide that seems to target the gut is a promising candidate on the horizon.

Development of intestinal immunoglobulin absorption and enzyme activities in neonatal pigs is diet dependent

Uptake of colostrum just after birth is essential to stimulate intestinal growth and function, and in many species, including pigs, colostrum also provides immunological protection via the absorption of immunoglobulin G (IgG). In this study, intestinal growth, IgG absorptive capacity and enzyme activities were investigated in newborn pigs in response to different diets. Newborn piglets were bottle-fed porcine colostrum (PC), bovine colostrum (BC), porcine plasma (PP), porcine milk (PM), bovine colostrum containing porcine plasma (BCP) or a milk replacer (MR) every 3 h (15 mL/kg) for up to 2 d. Bovine serum albumin (BSA) was added to the diets as a macromolecule marker. The percentage of absorbed BSA just after birth was highest for piglets fed the PC diet (30-50%), lower for those fed the BC and BCP diets (23-30%) and lowest for the PP, PM and MR diet-fed piglets (7-20%, P < 0.05 relative to those fed colostrum). Porcine IgG was absorbed more efficiently than bovine IgG. Intestinal closure occurred earlier in MR and BCP piglets (within 12 h after birth) than in PC pigs. At 2 d of age, intestinal mucosal weight (+120% increase from birth) and villus morphology were similar in the PC, BCP and MR groups. All 3 groups also had increased aminopeptidase A activity compared with values at birth (+100% increase). Compared with PC pigs, the BCP group had higher sucrase and maltase activities (+50% and +200%, respectively) and lower aminopeptidase N activity (-50%, P < 0.05). Similarly, MR pigs showed elevated sucrase activity (+40%) and lowered maltase, lactase and aminopeptidase N activities (-20% to -50%, P < 0.05) compared with PC pigs. We conclude that porcine and bovine colostrum contain factors that stimulate the intestinal endocytotic and enzymatic capacity in newborn pigs. A milk replacer can produce normal gut growth, but may be inefficient in mediating normal macromolecule transport and disaccharidase activity. Bovine colostrum mixed with porcine plasma proteins may be a useful substitute for porcine colostrum in artificial rearing of newborn pigs.

Oral IGF-I alters the posttranslational processing but not the activity of lactase-phlorizin hydrolase in formula-fed neonatal pigs

To determine the cellular mechanism whereby oral insulin-like growth factor I (IGF-I) increases intestinal lactase-phlorizin hydrolase (LPH) activity, we studied 2-d-old pigs fed cow's milk formula (control, n = 5), formula + low IGF-I (0.5 mg/L; n = 6) or formula + high IGF-I (12.0 mg/L, n = 6) for 15 d. On d 15, intestinal protein synthesis and lactase processing were measured in vivo in fed pigs using a 6-h intravenous, overlapping infusion of multiple stable isotopes (2H(3)-Leu, 13C(1)-Leu, 13C(1)-Phe, 2H(5)-Phe, 13C(6)-Phe and 13C(9)-Phe). Morphometry and cell proliferation also were measured in the jejunum and ileum. Neither dose of IGF-I affected the masses of wet tissue, protein or DNA, or the villus height, cell proliferation or LPH-specific activity. Oral IGF-I decreased the synthesis and abundance of prolactase-phlorizin hydrolase (pro-LPH), but increased brush-border (BB)-LPH synthesis in the ileum. The BB-LPH processing efficiency was twofold to threefold greater in IGF-fed than in control pigs. In all pigs, villus height and the total mucosal and specific activity of LPH activity were greater in the ileum than in the jejunum, yet the synthesis of BB-LPH were significantly lower in the ileum than in the jejunum. We conclude that oral IGF-I increases the processing efficiency of pro-LPH to BB-LPH but does not affect LPH activity. Moreover, the posttranslational processing of BB-LPH is markedly lower in the ileum than in the jejunum.

Intestinal protein and LPH synthesis in parenterally fed piglets receiving partial enteral nutrition and enteral insulinlike growth factor 1

BACKGROUND

Providing partial enteral nutrition (PEN) supplemented with insulinlike growth factor-1 (IGF-1) to parenterally fed piglets increases lactase-phlorizin hydrolase (LPH) activity, but not LPH mRNA. The current aim was to investigate potential mechanisms by which IGF-1 up-regulates LPH activity.

METHODS

Newborn piglets (n = 15) received 100% parenteral nutrition (TPN), 80% parenteral nutrition + 20% parenteral nutrition (PEN), or PEN + IGF-1 (1.0 mg. kg-1. d-1) for 7 days. On day 7, [2H3]-leucine was intravenously administered to measure mucosal protein and brush border LPH (BB LPH) synthesis.

RESULTS

Weight gain, nutrient intake, and jejunal weight and length were similar among the treatment groups. Partial enteral nutrition alone increased mucosal weight, villus width and cross-sectional area, LPH activity, mRNA expression, and high mannose LPH precursor (proLPHh) abundance compared with TPN (P<0.05). Insulinlike growth factor-1 further increased mucosal weight, LPH activity, and LPH activity per unit BB LPH approximately twofold over PEN alone (P < 0.05) but did not affect LPH mRNA or the abundance of proLPHh (one of the LPH isoforms) or mature LPH. Isotopic enrichment of [2H3]-leucine in plasma, mucosal protein, and LPH precursors, and the fractional and absolute synthesis rates of mucosal protein and LPH were similar among the treatment groups. Insulinlike growth factor-1 treatment increased total mucosal protein synthesis (60%, P < 0.05) but not LPH synthesis compared with the other two groups.

CONCLUSIONS

Because IGF-1 did not affect the fractional synthesis rate of either mucosal protein or LPH, the authors suggest that enteral IGF-1 increases mucosal protein mass and LPH activity by suppressing mucosal proteolytic degradation.